Aqueous dispersion of a biodegradable polyester and its use thereof

ABSTRACT

The aqueous dispersion of a biodegradable aliphatic-aromatic polyester is useful as a binder for nonwovens and for coating paper.

The present invention relates to a polyester dispersion comprising waterand a biodegradable, aliphatic-aromatic copolyester, a process for itspreparation and its use as a binder for nonwovens and for coating paper.The present invention further relates to the nonwoven produced using thepolyester dispersion of the invention, a process for its production andits use.

The biodegradable copolyesters used in the aqueous polyester dispersionof the invention contain repeat units derived both from aromaticcarboxylic acids or derivatives thereof and from aliphatic carboxylicacids and derivatives thereof and are known per se.

For instance, U.S. Pat. No. 5,446,079 and the parallel internationalapplication WO 92/09654 describe a linear, random, semicrystallinealiphatic-aromatic copolyester having a limiting viscosity number ofabout 0.5 to 1.8 dl/g, measured in 60/40 w/w phenol/tetrachloroethane ata concentration of 0.5 g/100 ml and at a temperature of 25° C., theproportion of units derived from aromatic carboxylic acids being from 5to 65 mol % and the proportion of repeat units derived from aliphaticcarboxylic acids being from 95 to 35 mol %, in each case based on thetotal amount of repeat units derived from carboxylic acids. Not only thebiodegradability of such polyesters also their use as moldings, films,etc. are described.

DE-A-44 32 161 describes biodegradable polyesters which are degraded inthe natural environment and under the action of microorganisms which arecondensed (a) from an aliphatic polyol and an aromatic polyol and analiphatic polycarboxylic acid or (b) from an aliphatic polyol,optionally alongside an aromatic polyol, and an aromatic polycarboxylicacid as well as simultaneously aliphatic polycarboxylic acid, or (c)from an aromatic hydroxymonocarboxylic acid and an aliphatichydroxymonocarboxylic acid as monomer components, the units derived fromthe monomer components being in random or alternating arrangement.

In addition, the biodegradable polyesters used herein are likewisedescribed per se in a number of commonly assigned applications (DE-A-4440 858, DE-A-44 40 850, DE-A-44 40 837, DE-A-44 40 836, DE-A-195 00 757,DE-A-195 00 756, DE-A-195 00 755, DE-A-195 00 754, DE-A-195 00 185,DE-A-195 05 186).

However, none of these references describe polyester dispersionsutilizing these polyesters.

Polyester dispersions and their preparation are likewise known per se(see inter alia U.S. Pat. No. 3,546,008, EP-A-0 332 980 and EP-A-0 498156). For instance, U.S. Pat. No. 3,546,008 describes fibrous productstreated with a size comprising a linear polyester which disperses inwater. This polyester is prepared starting from at least one carboxylicacid, at least one diol, provided at least 20% of the diol ispolyethylene glycol, and a monomer having an SO₃ M group, where M ishydrogen or a metal ion. Copolyesters of the type contemplated hereinare not mentioned in this reference. Polyesters derived from carboxylicacid mixtures comprising hexahydroisophthalic acid and from a diol areexemplified. Such polyesters are not biodegradable, however.

EP-A-0 332 980 relates to a process for preparing aqueous polyesterdispersions by condensing aromatic dicarboxylic acids or esters with atleast one diol to form prepolymers having an acid number from 2 to 8.These prepolymers are subsequently reacted with at least one molecularweight enhancer compound to form polyesters having acid numbers of 40 to60 and the polyester is dispersed by addition of aqueous mixtures ofammonia and amines in a molar ratio of 10:1 to 1:10 to a polyester melthaving a temperature within the range from 150 to 210° C. The referencefurther relates to the use of these polyester dispersions as sizes forsizing filament warp yarns. The polyesters used in this reference, whichare based on aromatic dicarboxylic acids, have excellent mechanicalproperties, but virtually no biodegradability.

EP-A-0 498 156 describes aqueous polyesters for high solids bakingfinishes wherein the urethane-, carboxyl- and hydroxyl-functionalpolyester resin described has a hydroxyl number of 40 to 110 and aurethane group content of 6.5 to 11% by weight. Such polyesters haverelatively high tackiness and unsatisfactory mechanical strength and aretherefore unsuitable for the applications contemplated in thisinvention.

Nonwovens suitable for composting are known.

For instance, EP-A-0 591 821 describes a compostable nonwoven bondedwith from 5 to 100% by weight, based on the weight of the fiber used, ofan addition polymer which has a glass transition temperature of -70 to+40° C. and which is preparable by free-radical polymerization ofethylenically unsaturated monomers comprising 0.5 to 15% by weight ofN-alkylolamides of α,β-monoethylenically unsaturated carboxylic acidshaving 3 to 10 carbon atoms, acrylamidoglycolic acids,methacrylamidoglycolic acid and/or their ethers, esters or ether-esterswith alcohols having up to 12 carbon atoms in an aqueous medium in thepresence of a saccharide, and also its preparation and use.

DE-A-41 21 085 describes a biodegradable film or molded article preparedfrom a composition comprising 100 parts by weight of cellulose fibershaving a length of 3 mm or less and a diameter of 50 mm or less, 10 to600 parts by weight of a thermoplastic resin and 2 to 100 parts byweight of chitosan. Thermoplastic resins mentioned are polyvinylalcohols, polyurethanes and aliphatic polyesters. Here too the resultingbiodegradable articles generally lack mechanical strength, owing to thethermoplastic resins used, and, what is more, are frequently tacky.

Furthermore, Canadian Patent Application CA 2 057 669 describesbiodegradable aliphatic polyesters useful as binders for impregnating orcoating fibrous fabrics. These polyesters are admittedly, as brieflymentioned above, very readily biodegradable, but generally they possessinadequate mechanical properties and relatively poor processibility.

It is an object of the present invention to provide aqueousbiodegradable polyester dispersions possessing excellent mechanicalproperties combined with good processibility. In addition, thebiodegradability, i.e. the time to essentially complete degradation, ofthe copolyesters used and of the nonwovens treated therewith shall bevariable within a considerable time span.

We have found that this object is achieved by a polyester dispersioncomprising

(A) from 20 to 90% by weight of water, and

(B) from 10 to 80% by weight of a biodegradable copolyester (B)containing structural units derived from both aliphatic and aromaticcarboxylic acids or derivatives thereof, obtainable by reaction of amixture comprising

(a1) a mixture comprising

(a11) from 20 to 95 mol % of adipic acid or of an ester-formingderivative thereof or of a mixture of two or more thereof,

(a12) from 5 to 80 mol % of terephthalic acid or of an ester-formingderivative thereof or of a mixture of two or more thereof,

(a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of twoor more thereof,

the sum total of the individual mol %ages being 100,

(a2) a dihydroxy compound or an aminoalcohol or a mixture of two or morethereof,

the molar ratio of (a1) to (a2) being within the range from 0.4:1 to2.5:1,

(a3) from 0.01 to 10% by weight, based on mixture (a1), of a chainextender from the group consisting of the diisocyanates, divinyl ethersand the 2,2'bisoxazoline of the ##STR1## where R¹ is a single bond, a(CH₂)_(q) alkylene group, where q is 2, 3 or 4, or a phenylene group, orof a mixture of two or more thereof, and

(a4) from 0 to 20% by weight, based on mixture (a1), of a compoundhaving at least three groups capable of ester formation or of a mixtureof two or more thereof,

wherein

the repeat units derived from (a11) and (a12) carboxylic acid form arandom distribution, the copolyester has a viscosity number within therange from 5 to 450 ml/g (measured in 50/50 w/w o-dichlorobenzene phenolat a concentration of 0.5% by weight of copolyester at 25° C.), and theproportions of components (a13) and (a4) are not zero at the same time.

As used herein "biodegradable" describes the fact that the copolyestersare broken down over a suitable and verifiable period by environmentaleffects. Degradation is in general hydrolytic and/or oxidative, butpredominantly due to the action of microorganisms such as bacteria,yeasts, fungi and algae. Degradation can also take place enzymatically,as described for example by Y. Tokiwa and T. Suzuki in Nature 270(1977), 76-78. The present invention makes it possible, throughappropriate selection of the ratio between repeat units derived fromaliphatic carboxylic acids and repeat units derived from aromaticcarboxylic acids, to vary the rate of the biological degradationprocess, i.e. the time to essentially complete degradation of thepolyesters used in accordance with this invention. The rule of thumb isthat the rate of biodegradation of the copolyesters increases with theproportion of repeat units derived from aliphatic carboxylic acids.Furthermore, the rate of bio-degradation of the copolyesters increaseswith the proportion of segments having an alternating sequence of repeatunits derived from aliphatic and aromatic carboxylic acids orderivatives thereof.

The polyester dispersion of the invention comprises from about 10 toabout 80, preferably from about 20 to about 60, in particular from about20 to about 40,% by weight of solids, i.e. of the copolyester usedaccording to this invention.

The aliphatic dicarboxylic acid which is useful for the purposes of thepresent invention is adipic acid.

Suitable ester-forming derivatives for the adipic acid are in particularthe di-C₁ -C₆ -alkyl esters, for example the dimethyl, diethyl,dipropyl, dibutyl, dipentyl and dihexyl esters.

The adipic acid or ester-forming derivatives thereof can be used aloneor as a mixture of two or more thereof.

The proportion of adipic acid or its ester-forming derivatives isgenerally within the range from about 20 to 95, preferably from about 30to about 70, in particular from about 40 to about 60, mol %, based onthe total amount of components (a11) to (a13).

The aromatic dicarboxylic acid used according to the invention isterephthalic acid or an ester-forming derivative thereof. Especially thedi-C₁ -C₆ -alkyl esters, for example the dimethyl, diethyl, dipropyl,dibutyl, dipentyl and dihexyl esters, are suitable.

The terephthalic acid or its ester-forming derivatives (a12) can be usedindividually or as a mixture of two or more thereof.

The proportion of terephthalic acid or ester-forming derivatives thereofis generally within the range from about 5 to about 80, preferably fromabout 30 to about 70, in particular from about 40 to about 60, mol %,based on the total amount of components (a11) to (a13).

The sulfonate compound (a13) used in this invention is customarily analkali metal or alkaline earth metal salt of a sulfonate-functionaldicarboxylic acid or its ester-forming derivatives, preferably alkalimetal salts of 5-sulfoisophthalic acid or mixtures thereof, especiallythe sodium salt. The proportion of sulfonate compound (a13) is withinthe range from 0 to about 10, preferably from 0 to about 5, inparticular from about 3 to about 5, mol %, based on the total amount ofcomponents (a11) to (a13).

The sulfonate compounds can be used individually or as a mixture of twoor more thereof.

Component (a2) of this invention is a dihydroxy compound or aminoalcoholor a mixture of two or more thereof. In principle, any diols oraminoalcohols known in ester-making can be used.

In general, however, component (a2) is selected from (a21) alkanediolshaving from 2 to 12 carbon atoms, preferably 4 to 6 carbon atoms, orcycloalkanediols having from 5 to 10 carbon atoms, (a22) polyetherdiols,i.e. dihydroxy compounds containing ether groups, and (a23)aminoalcohols having from 2 to 12 carbon atoms, preferably from 2 to 4carbon atoms, and also aminocycloalcohols having from 5 to 10 carbonatoms.

Specific examples are ethylene glycol, 1,2-propanediol, 1,3-propanediol,1,2-butanediol, 1,4-butanediol, 1,5-pentanediol,2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol,2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol,2,2,4-trimethyl-1,6-hexanediol, especially ethylene glycol,1,3-propanediol, 1,4-butanediol and 2,2-dimethyl-1,3-propanediol(neopentylglycol); cyclopentanediol, 1,4-cyclohexanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1,4-cyclohexanedimethanol and 2,2,4,4-tetramethyl-1,3-cyclobutanediol;

diethylene glycol, triethylene glycol, polyethylene glycol,polypropylene glycol and polytetrahydrofuran, especially diethyleneglycol, triethylene glycol and polyethylene glycol, or mixtures thereof,or compounds which have a differing number of ether units, for examplepolyethylene glycol which contains propylene units and can be obtainedfor example by conventional polymerization of first ethylene oxide andthen propylene oxide. The molecular weight (Mn) of the polyethyleneglycols which can be used is generally within the range from about 250to about 8000, preferably within the range from about 600 to about 3000,g/mol;

4-aminomethylcyclohexanemethanol, 2-aminoethanol, 3-aminopropanol,4-aminobutanol, 5-aminopentanol, 6-aminohexanol; aminocyclopentanol andaminocyclohexanol; or mixtures thereof.

The dihydroxy compounds or aminoalcohols can be used individually or asa mixture of two or more thereof.

The molar ratio of (a1) to (a2) is generally chosen within the rangefrom about 0.4:1 to about 2.5:1, preferably within the range from about0.5:1 to about 1.5:1, more preferably within the range from about 0.5:1to about 1.2:1, especially within the range from about 0.5:1 to about1:1.

The molar ratio of (a1) and (a2) in the isolated copolyester followingthe removal of the desired amount of excess component (a2) is within therange from about 0.4:1 to about 1.5:1, preferably within the range fromabout 0.5:1 to about 1.2:1, especially within the range from about 0.5:1to about 1:1.

The proportion of chain extenders (a3) is within the range from about0.01 to about 10, preferably within the range from about 0.05 to about5, more preferably within the range from about 0.07 to about 4,especially within the range from about 0.1 to about 1%, by weight, basedon mixture (a1).

Suitable chain extenders (a3) for use herein are diisocyanates, forexample toluylene 2,4-diisocyanate, toluylene 2,6-diisocyanate, 4,4'-and 2,4'-diphenylmethane diisocyanate, naphthylene 1,5-diisocyanate,xylylene diisocyanate, hexamethylene diisocyanate, isophoronediisocyanate and methylenebis(4-isocyanato-cyclohexane), especiallyhexamethylene diisocyanate; divinyl ethers, for example 1,4-butanedioldivinyl ether, 1,6-hexanediol divinyl ether and1,4-cyclohexane-dimethanol divinyl ether; and also 2,2'-bisoxazolines ofthe general formula (I) ##STR2##

The latter are generally obatinable by the process of Angew. Chem. Int.Edit. 11 (1972), 287-288. Particularly preferred bisoxazolines are thosein which R¹ is a single bond, a (CH₂)_(q) -alkylene group having q=2, 3or 4 such as methylene, 1,2-ethanediyl, 1,3-propanediyl,1,2-propanediyl, 1,4-butanediyl or a phenylene group. Particularpreference is given to 2,2'-bis(2-oxazoline), bis(2-oxazolinyl)methane,1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane,1,4-bis(2-oxazolinyl)butane, 1,4-bis(2-oxazolinyl)benzene,1,2-bis(2-oxazolinyl)benzene and 1,3-bis(2-oxazolinyl)benzene.

The chain extenders (a3) can also be used as a mixture of two or morethereof.

This invention further contemplates the use of a compound having atleast three groups capable of ester formation, (a4), or of a mixture oftwo or more thereof, in an amount, if present at all, within the rangefrom about 0.01 to about 20, preferably from about 1 to about 10, morepreferably from about 3 to about 7, especially from about 3 to about 5%,by weight, based on mixture (a1).

The compounds used as compounds (a4) preferably contain from 3 to 10functional groups capable of forming ester bonds. Particularly preferredcompounds (a4) have from 3 to 6 functional groups of this kind in themolecule, especially from 3 to 6 hydroxyl groups and/or carboxyl groups.Particular preference is given to using tri- and/or tetrafunctionalcarboxylic acids or derivatives thereof. Specific examples are tartaricacid, citric acid, malic acid, trimethylolpropane, trimethylolethane,pentaerythritol, polyethertriols, glycerol, trimesic acid, trimelliticacid, trimellitic anhydride, pyromellitic acid, pyromellitic dianhydrideand hydroxyisophthalic acid.

By including the chain extenders (a3) and/or the compounds (a4) it ispossible for example to modify the melt viscosity, the limitingviscosity number or the molecular weight in a desired manner comparedwith polyesters without added chain extenders (a3) and/or compounds(a4), to raise the limiting viscosity number and the molecular weightaccordingly and so vary the mechanical properties of the polyesters inaccordance with the particular application.

Here it has to be noted that, according to the invention, at least onecomponent (a13) and/or (a4) has to be present at all times in order thatthe copolyester may have free acid groups.

If desired, the copolyesters (B) can have as further componenttrifunctional isocyanate compounds which comprise isocyanurate and/orbiuret groups having a functionality of not less than 3.

In a further embodiment, the present invention relates to a polyesterdispersion comprising

(A) from 20 to 90% by weight of water, and

(B) from 10 to 80% by weight of a biodegradable copolyester (B1)containing structural units derived from both aliphatic and aromaticcarboxylic acids or derivatives thereof,

obtainable by reaction of a mixture comprising

(a1) a mixture comprising

(a11) from 20 to 95 mol % of adipic acid or of an ester-formingderivative thereof or of a mixture of two or more thereof,

(a12) from 5 to 80 mol % of terephthalic acid or of an ester-formingderivative thereof or of a mixture of two or more thereof,

(a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of twoor more thereof,

the sum total of the individual mol %ages being 100,

(a2) a dihydroxy compound or an aminoalcohol or a mixture of two or morethereof,

the molar ratio of (a1) to (a2) being within the range from 0.4:1 to2.5:1,

(a3) from 0 to 10% by weight, based on mixture (a1), of a chain extenderfrom the group consisting of the diisocyanates, dinvinyl ethers and the2,2'-bisoxazolines of the ##STR3## where R¹ is a single bond, a(CH₂)_(q) alkylene group, where q is 2, 3 or 4, or a phenylene group, orof a mixture of two or more thereof,

(a4) from 0 to 20% by weight, based on mixture (a1), of a compoundhaving at least three groups capable of ester formation or of a mixtureof two or more thereof,

(b1) from 0.01 to 100% by weight, based on mixture (a1), of ahydroxycarboxylic acid (b1) defined by the following formula IIa or IIb##STR4## where p is an integer from 1 to 1500, r is 1, 2, 3 or 4, and Gis phenylene, --(CH₂)_(n) --, where n is 1, 2, 3, 4 or 5, --C(R)H-- or--C(R)HCH₂ --, where R is methyl or ethyl,

or of a mixture of two or more thereof,

wherein the repeat units derived from the (cyclo)-aliphatic and aromaticcarboxylic acid form a random distribution, the copolyester has aviscosity number within the range from 5 to 450 ml/g (measured in 50/50w/w o-dichlorobenzene/phenol at a concentration of 0.5% by weight ofcopolyester at 25° C.), and the proportions of components (a13) and (14)are not zero at the same time.

In the above formula, p is preferably from 1 to about 1000, r ispreferably 1 or 2, and n is preferably 1 or 5.

The level of hydroxycarboxylic acid (b1) in the reaction mixture ispreferably within the range from about 0.1 to 80% by weight, based onmixture (a1).

Hydroxycarboxylic acid (b1) is preferably glycolic acid, D-lactic acid,L-lactic acid, D,L-lactic acid, 6-hydroxy-hexanoic acid, their cyclicderivatives such as glycolide (1,4-dioxane-2,5-dione), D- or L-dilactide(3,6-dimethyl-1,4-dioxane-2,5-dione), p-hydroxybenzoic acid and alsotheir oligomers and polymers such as 3-polyhydroxybutyric acid,polyhydroxyvaleric acid, polylactide (obtainable for example as EcoPLA®(fr. Cargill)) and also a mixture of 3-polyhydroxybutyric acid andpolyhydroxyvaleric acid (the latter is obtainable from Zeneca under thename of Biopol®), and the above-defined low molecular weight and cyclicderivatives are used.

It is of course also possible to use mixtures of two or more of theabove-defined hydroxycarboxylic acids.

In a further embodiment, the use of cyclic derivatives of theabove-described hydroxycarboxylic acids (b1) in the reaction with thebiodegradable copolyester used according to the invention results,through a conventional ring-opening polymerization, in copolyesters ofthe above-defined type which contain block structures consisting of thecopolyester (B) used according to this invention which are in each caselinked together by at least one hydroxycarboxylic acid unit (b1) (rering-opening polymerization see Encyclopedia of Polymer Science andEngineering, Vol. 12, 2nd Ed., John Wiley & Sons, 1988, pages 36-41).

Copolyesters whose use is particularly preferred in the presentinvention have the following composition as regards components (a11),(a12) and (a2), although it has to be taken into account that thesecopolyesters can not only have sulfonic acid groups but also contain thechain extenders and/or compounds defined as components (a3) and (a4).The parenthetical values following the respective component correspondto the proportion of this component, expressed in mol %:

terephthalic acid (40)--adipic acid (60)--butanediol (100),

terephthalic acid (30)--adipic acid (70)--butanediol (100).

The copolyesters used according to the invention are characterized bythe following features:

They have a viscosity number within the range from about 5 to 450 ml/g,preferably within the range from about 50 to about 350 ml/g, morepreferably within the range from about 100 to about 350 ml/g, especiallywithin the range from about 200 to about 350 ml/g, in each case measuredin 50/50 w/w o-dichlorobenzene/phenol at a concentration of 0.5% byweight of copolyester at 25° C.

The copolyesters used according to the invention further possess bothhydroxyl and carboxyl end groups.

The hydroxyl number of the copolyesters used according to the inventionis within the range from 0 to about 30, preferably within the range from0 to about 20, in particular within the range from 0 to about 10.

For further details of the (cyclo)aliphatic dicarboxylic acids, aromaticdicarboxylic acids, diols and/or amino-alcohols usable in this inventionand also of the further components (a3), (a4) and (b1) reference is madeto the commonly assigned patent applications mentioned at the beginningin the discussion of background art and to U.S. Pat. No. 5,446,079, orthe parallel Application WO92/09654, incorporated herein by referencefor the copolyesters and their preparation described therein.

None the less, the preparation of the copolyesters used according to theinvention will now be briefly described.

This preparation of polyesters is known in principle (Sorensen andCampbell, Preparative Methods of Polymer Chemistry, IntersciencePublishers, Inc., New York, 1961, pages 111-127; Encyclopedia of PolymerScience and Engineering, Vol. 12, 2nd Ed., John Wiley & Sons, 1988,pages 1-75; Kunststoffhandbuch, Vol. 3/1, Carl Hanser Verlag, Munich,1992, pages 15-23 (Herstellung von Polyestern); and also theaforementioned patent applications.

For instance, the reaction of (a1)-comprised dimethyl esters ofdicarboxylic acids (a11/a12) with component (a2) ("transesterification")and optionally components (a13) and/or (b1) can be carried out attemperatures within the range from about 160 to about 230° C. in themelt at atmospheric pressure, preferably under an inert gas atmosphere.

It is advantageous to prepare the biodegradable copolyester usedaccording to the invention using a molar excess of component (a2), basedon the dicarboxylic acids used, for example up to an excess of not morethan about 2.5-fold, generally up to about 1.5-fold.

The preparation of the abovementioned copolyester is customarilyeffected in the presence of suitable conventional catalysts such asmetal compounds based on the following elements such as Ti, Ge, Zn, Fe,Mn, Co, Zr, V, Ir, La, Ce, Li and Ca, preferably organometalliccompounds based on these metals such as salts of organic acids,alkoxides, acetylacetonates and the like, especially on the basis of Zn,Sn and Ti.

The reaction of components (a1), (a2) and optionally (b1) is generallycarried out under reduced pressure or in an inert gas stream, forexample under nitrogen, and under continued heating to a temperaturewithin the range from 180 to 260° C. until the desired molecular weighthaving regard to the desired molar ratio of carboxyl end groups tohydroxyl end groups. Subsequently, (a3) and/or (a4) can generally beadded at atmospheric pressure at a temperature within the range fromabout 50 to about 200° C., preferably under an inert gas, to continuethe reaction.

To avoid undesirable degradation and/or side reactions, this processstep can, if desired, also be carried out in the presence ofstabilizers, the amount of which should be kept as low as possible andis generally within the range from 0.1 to 200 ppm, based on thecopolyester. Examples of such stabilizers are phosphorus compounds asdescribed for example in EP-A 13 461, U.S. Pat. No. 4,328,049 and theabovementioned commonly assigned patent applications.

The present invention accordingly further provides a process forpreparing the aqueous polyester dispersion of the invention, whichcomprises

(i) preparing a copolyester (B) in a conventional manner by reacting amixture comprising

(a1l) a mixture comprising

(a11) from 20 to 95 mol % of adipic acid or of an ester-formingderivative thereof or of a mixture of two or more thereof,

(a12) from 5 to 80 mol % of terephthalic acid or of a mixture of two ormore thereof,

(a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of twoor more thereof, the sum total of the individual mol %ages being 100 mol%,

(a2) a dihydroxy compound or an aminoalcohol or a mixture of two or morethereof,

the molar ratio of (a1) to (a2) being within the range from 0.4:1 to2.5:1,

(a3) from 0.01 to 10% by weight, based on mixture (a1), of a chainextender from the group consisting of the diisocyanates, dinvinyl ethersand the 2,2'-bisoxazolines of the ##STR5## where R¹ is a single bond, a(CH₂)_(q) alkylene group, where q is 2, 3 or 4, or a phenylene group, orof a mixture of two or more thereof, and

(a4) from 0 to 20% by weight, based on mixture (a1), of a compoundhaving at least three groups capable of ester formation or of a mixtureof two or more thereof,

and performing the reaction in such a way that

the repeat units derived from (a11) and (a12) form a randomdistribution, the copolyester has a viscosity number within the rangefrom 5 to 450 ml/g (measured in 50/50 w/w o-dichlorobenzene/phenol at aconcentration of 0.5% by weight of copolyester at 25° C.), and theproportions of components (a13) and (a4) are not zero at the same time;

(ii) neutralizing and dispersing the resulting copolyester (B) in anaqueous medium using a suitable neutralizer.

The present invention further provides a process for preparing thepolyester dispersion of the invention, which comprises

(i) preparing a copolyester (Bl) in a conventional manner by reacting amixture comprising

(a1) a mixture comprising

(a11) from 20 to 95 mol % of adipic acid or of an ester-formingderivative thereof or of a mixture of two or more thereof,

(a12) from 5 to 80 mol % of terephthalic acid or of a mixture of two ormore thereof,

(a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of twoor more thereof,

the sum total of the individual mol %ages being 100,

(a2) a dihydroxy compound or an aminoalcohol or a mixture of two or morethereof,

the molar ratio of (a1) to (a2) being within the range from 0.4:1 to2.5:1,

(a3) from 0 to 10% by weight, based on mixture (a1), of a chain extenderfrom the group consisting of the diisocyanates, divinyl ethers and the2,2'bisoxazoline of the ##STR6## where R¹ is a single bond, a (CH₂)_(q)alkylene group, where q is 2, 3 or 4, or a phenylene group, or of amixture of two or more thereof, and

(a4) from 0 to 20% by weight, based on mixture (a1), of a compoundhaving at least three groups capable of ester formation or of a mixtureof two or more thereof,

(b1) from 0.01 to 100% by weight, based on mixture (a1), of ahydroxycarboxylic acid (b1) defined by the following formula IIa or IIb##STR7## where p is an integer from 1 to 1500, r is 1, 2, 3 or 4, and Gis phenylene, --(CH₂)_(n) --, where n is 1, 2, 3, 4 or 5, --C(R)H-- or--C(R)HCH₂ --, where R is methyl or ethyl, or of a mixture of two ormore thereof,

and performing the reaction in such a way that the repeat units derivedfrom the (cyclo)aliphatic and aromatic carboxylic acid form a random oralternating distribution, the copolyester has a viscosity number withinthe range from 5 to 450 ml/g (measured in 50/50 w/wo-dichlorobenzene/phenol at a concentration of 0.5% by weight ofcopolyester at 25° C.), and the proportions of components (a13) and (a4)are not zero at the same time;

(ii) neutralizing and dispersing the resulting copolyester (B1) in anaqueous medium using a suitable neutralizer.

In the two processes of the invention, the preparation of copolyester Bor copolyester B1 in step (i) is carried out as extensively discussedabove.

Thereafter the copolyester obtained as per step (i), generally as a hotmelt having a temperature within the range from about 150 to about 230°C., is admixed with an aqueous solution or dispersion of a neutralizer.The amount of neutralizer added is chosen so that the neutralizer isable to effect partial or complete neutralization of the acid groups,"partial neutralization" in the context of the present invention meaninga degree of neutralization within the range from about at least 70% ofthe carboxyl groups present in the copolyester. Water is generally addedin such an amount as to produce an aqueous polyester dispersion having apolyester content within the range from about 10 to about 80% by weight,preferably within the range from about 20 to about 60% by weight. Theneutralizer can also be added in excess.

As stated above, the mixture of water and a neutralizer is added to thepolyester melt at temperatures of the melt within the range from about150 to about 230° C., preferably at temperatures from about 150 to about200° C. However, the temperature should not be below 150° C., sinceotherwise there is a risk of not obtaining a fine dispersion of thepolyester in water. The aqueous polyester dispersion can also beprepared from the melt by first slowly adding up to about half theamount of water required, then adding the neutralizer and finally addingthe rest of the water. As the water, or mixture of water andneutralizer, is added to the melt, the temperature thereof decreases.

On completion of the addition of the neutralizer/water mixture, thetemperature of the resulting polyester dispersion is generally withinthe range from about 70 to about 100° C. The polyester dispersionobtained in this way is then stirred for from 2 to 12, preferably from 4to 6, hours, optionally at an elevated temperature of up to 95° C., andthen cooled down to ambient temperature.

The neutralizer used can in general be a traditional neutralizer.Specific examples are ammonia, triethylamine, triethanolamine,monoethanolamine, diethanolamine, N-methyldiethanolamine, morpholine,N-methylmorpholine, 2-amino-2-methyl-1-propanol and mixtures of two ormore thereof. Preference is given to using monoethanolamine,diethanolamine, N-methylmorpholine, methyldiethanolamine and ammonia.Alkali metal hydroxides such as, for example, sodium hydroxide ofpotassium hydroxide can also be used, but are less preferable.

It is further possible, on completion of the dispersing, to distil someof the water back out in order that the solids content may be maximized.

Furthermore, on completion of step (i), the resulting melt can first beadmixed with a suitable organic solvent, for example methyl ethylketone, tetrahydrofuran or acetone, and the polymer dissolved therein,then, as per step (ii), admixed with a neutralizer and water toneutralize and disperse and subsequently subjected to a vacuumdistillation to distil the organic solvent, which should bewater-miscible or at least water-dispersible, back out, if desiredtogether with excess water.

The process of the invention affords aqueous polyester dispersionshaving a solids content from about 10 to about 80% by weight, preferablyfrom about 20 to about 60% by weight.

In addition, the present invention provides for the use of theabove-described polyester dispersions as binders for biodegradablenonwovens, as coatings for paper and as spray mulch.

Suitable materials for nonwoven base webs are fibers which arebiodegradable. These are generally fibers having a diameter from about0.002 to about 0.1 mm, preferably from about 0.01 to about 0.05 mm,which can usually be ascertained with the aid of electron micrographs.

In general, the fibers used are natural fibers of cellulosic origin,such as viscose fibers or pulp fibers, or synthetic fibers, such asaliphatic polyester fibers, for example based on copolymers of3-hydroxybutyrate, 3-hydroxyvalerate and 4-hydroxyvalerate, as describedin EP-A 466 050, or those based on aliphatic dicarboxylic acids, forexample adipic acid. In addition, it is also possible to use syntheticfibers based on aliphatic-aromatic polyesters as described herein.

Suitable cellulose fibers are fibers obtained from cellulose,hemicellulose or lignocellulose, obtained from wood, straw, cotton,jute, bamboo or bagasse, and cellulose produced by bacteria.

The formation of webs from the fibers is common knowledge and describedfor example in Rompp, Chemie Lexikon, Georg Thieme Verlag,Stuttgart--New York, 9th Edition, p. 4450. The fiber webs in questioncan be random fiber webs or preferably oriented fiber webs with orwithout mechanical preconsolidation, for example in the form ofneedling, entangling or stitch bonding.

The fiber webs are bonded using from about 5 to 100, preferably fromabout 11 or more, especially from about 15 to about 50, more preferablyfrom about 20 to about 35%, by weight, based on the amount of fiber webused, of the copolyester.

The consolidation of the fiber webs using the polyesters is effectedaccording to known methods (as described for example in Ullmann'sEncyklopadie der technischen Chemie, 4th Edition, Vol. 23, 1983, pages738 to 742). The fiber web is customarily contacted or saturated withthe polyester dispersion by bath impregnation, foam impregnation,spraying, padding or printing. The dispersion can if necessary beadditionally diluted with water or else thickened with customarythickeners to obtain the desired processing viscosity. The treatment ofthe web with the dispersion is generally followed by an operation ofdrying and heating the resulting nonwoven fabric. The drying conditionsdepend on the type of dryer used; the drying temperature is customarilywithin the range from 100 to 230° C., and the drying/heating is carriedout for a period within the range from about 10 s to about 60 min.

The present invention accordingly also provides a non-woven comprisingas binder 5 to 100% by weight, based on the weight of the fibers used,of a copolyester as defined above or of a copolyester prepared by aprocess as defined above.

In a preferred embodiment, this nonwoven further comprises from 2 to100% by weight of chitosan, based on 100 parts by weight of the fiberused.

Chitosan is a product obtained by deacetylation of chitin present in themycelium or shells of crustaceans such as crabs or lobsters. Themolecular weight and the final degree of acetylation of chitosan used inthe present invention are not subject to specific restrictions. However,for reasons of solubility, a final degree of acetylation of at least 60%is desirable.

As observed above, the amount of chitosan is within the range from 2 to100% by weight, preferably within the range from 5 to 80% by weight,based on 100 parts by weight of the fibers used. An amount of chitosanoutside the aforementioned range is not advantageous, since the wetstrength suffers. The at least 5% by weight of binder, based on theweight of the fibers used, are necessary to confer the desiredflexibility on the web. Experimental work on webs coated or bonded withchitosan exclusively has shown that such webs are exceedingly rigid andconsequently not usable for many applications.

The present invention further provides a process for producing anonwoven, which comprises contacting the fibers with a polyesterdispersion as defined or a polyester dispersion prepared by a process asdefined in such an amount that the level of copolyester in the bondedfabric is from 5 to 100% by weight, based on the weight of the fibersused. Of course, it is also possible to use mixtures of two or more ofthe above polyester dispersions.

To produce the nonwoven of the invention which further compriseschitosan as binder, the process of the invention includes a further stepof preparing an aqueous solution of an acidic salt of chitosan andcontacting this solution with the fibers before or during or togetherwith the aqueous dispersion of the copolyester.

On completion of the contacting impregnation step, the resultingnonwoven is dried.

Before drying, the nonwoven thus obtained can be additionally shaped, sothat it is also possible to produce a shaped article from the nonwovenof the invention, which is subsequently dried. For example, theas-obtained nonwoven can be spread out on a suitable surface such as aglass plate to obtain a shaped article in the form of a free orsupported film.

In the practice of the foregoing process for producing the preferredembodiment of the chitosan-comprising nonwoven according to theinvention, it is advisable to use chitosan in the form of an acidic saltsuch as hydrochloride or as a similar inorganic acidic salt or formate,acetate, lactate or as a similar organic acidic salt.

In addition, the nonwoven of the invention may include one or moreadditives, for example a filler or a dye or a mixture of two or morethereof, in which case not only organic fillers, for example starch, butalso inorganic fillers, for example silicon dioxide, are used.

The nonwovens of the invention are notable for good compostabilitycoupled with favorable performance characteristics, especially highmechanical strength. They exhibit, inter alia, good dry strength, highwet strength and a soft hand. It must be considered surprising,especially in relation to the additional use of chitosan as per thepreferred embodiment of the nonwovens of this invention, that theaddition of a polyester dispersion greatly increases the flexibility ofthe resulting nonwoven.

The nonwoven of the invention can be used as a compostable film,compostable molding and for manufacturing diapers or wipes.

The invention will now be more particularly described with reference tosome examples.

INVENTIVE EXAMPLES 1 TO 3 AND COMPARATIVE EXAMPLE General Method ofPolyester Production

To prepare polyesters Inv. 1, Inv. 2 and Inv. 3, the amounts of aromaticdicarboxylic acids, adipic acid and dihydroxy compound specified inTable 1 were introduced into a reaction vessel together with 100 ppm oftetrabutyl orthotitanate (TBOT), the molar ratio between alcoholcomponents and acid component being 1.85. The reaction mixture washeated to a temperature within the range from 170° C. to 190° C. andreacted at that temperature for 3-4 hours. The temperature was thenraised to 240° C., and excess dihydroxy compound was distilled off underreduced pressure. The OH number of the copolyester obtained wasdetermined and adjusted to 20 by addition of a dihydroxy compound.

General Method of Dispersion Production

The polyesters Inv. 1 to Inv. 3 prepared by the above general methodwere melted in a reaction vessel. The resulting polyester melt wasadmixed with an amount of pyromellitic dianhydride (PMDA) correspondingto the OH number and stirred at 50 rpm. The temperature was slowlyraised to 180° C., and hexamethylene diisocyanate (HDI) was added in 0.5ml increments. The torque was measured. As soon as the torque reached50% (measured with an RE162 laboratory stirrer from Janke & Kunkel), 300ml of methyl ethyl ketone (MEK) were added to the melt and the polymerwas then dissolved in MEK. After the polymer solution had been cooleddown to 40° C., the acid groups of the polyester were neutralized withan appropriate amount of ethanolamine. The solution was then admixedwith 1 l of water and vigorously stirred. 200 ml of acetone were addedto the resulting dispersion. The acetone and the MEK were then distilledoff at 60° C. under reduced pressure.

Viscose nonwovens were impregnated with these dispersions in a dip bathprocess, dried at 150° C. for 2 minutes and then tested in respect oftheir application properties.

The results of these tests and the composition of the copolyesterobtained (without HDI and PMDA) are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    TS        IS  ADS BD  DEG Rkr · tr                                                                  Rkr · naβ                          mol % mol % mol % mol % mol % N/50 mm Nm                                    __________________________________________________________________________    Inv. 1                                                                              40  --  60  100 --  38   13                                               Inv. 2 35 5 60  85 15 33 14                                                   Inv. 3 30 -- 70 100 -- 29 12                                                  Acronal ® -- -- -- -- -- 39 13                                            DS2331X                                                                       (comp.)                                                                     __________________________________________________________________________     Key to abbreviations used in the table:                                       TS: terephthalic acid;                                                        IS: isophthalic acid;                                                         ADS: adipic acid;                                                             BD: butanediol;                                                               DEG: diethylene glycol;                                                       Acronal ® DS2331X designates a commercially available acrylate            dispersion marketed by BASF;                                                  Rkr · tr: dry breaking strength (measured according to DIN           53857);                                                                       Rkr · naβ: wet breaking strength (measured according to ISO     90733).                                                                  

In the above inventive examples (Inv. 1 to Inv. 3), the amount ofcopolyester applied as binder was 33% by weight, based on the amount ofnonwoven used.

The nonwovens consolidated by treatment with the dispersion of theinvention had dry and wet strengths similar to those obtained with thedispersion Acronal® DS2331X, which consists of starch and a polyacrylateand is accordingly not biodegradable in respect of the polyacrylatecontent. In addition, however, they advantageously exhibitedbiodegradability.

The biodegradability of the polyester dispersions of the invention wasalso tested.

The following tests were carried out:

Film composting test

Polyester films produced in a thickness of 50 μm from the polyesterdispersion Inv. 2 by drying at 80° C. were buried in mature compost at58° C. and the degradation of the films was assessed by inspection.

The film prepared from the polyester dispersion Inv. 2 was almostcompletely decomposed after 6 weeks in the compost at 58° C.

CO₂ evolution test at 58° C. (conforming to ISO 14852) and aerobiccomposting test (conforming to ISO/CD 14855).

The dispersion Inv. 2 was tested for biodegradability in the CO₂evolution test at 58° C. This test measures the carbon dioxide producedby the process of biodegradation and the increase in biomass.

The dispersion Inv. 1 was tested for biodegradability or compostabilityin the aerobic composting test. This test measures the carbon dioxideproduced in the course of biodegradation.

The results of the two tests are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    TS     IS  ADS BD  DEG Biodegradab-                                             mol % mol % mol % mol % mol % ility Method                                  __________________________________________________________________________    Inv. 2                                                                           35  5   60   85 15  87% (CO.sub.2 +                                                                      CO.sub.2 evolu-                                         biomass) tion test                                                      Inv. 1 40 -- 60 100 -- 76% CO.sub.2 Aerobic                                          composting                                                                    test                                                                 __________________________________________________________________________

As can be seen from Table 2, almost 90% of the test substance used wasconverted into CO₂ and biomass.

We claim:
 1. A polyester dispersion comprising(A) from 20 to 90% by weight of water, and (B) from 10 to 80% by weight of a biodegradable copolyester (B) containing free acid groups and structural units derived from both aliphatic and aromatic carboxylic acids or derivatives thereof, obtained by reaction of a mixture comprising(a1) a mixture comprising(a11) from 20 to 95 mol % of adipic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof, (a12) from 5 to 80 mol % of an terephthalic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof, (a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of two or more thereof, the sum total of the individual mol %ages being 100, (a2) a dihydroxy compound or an aminoalcohol or a mixture of two or more thereof, the molar ratio of (a1) to (a2) being within the range from 0.4:1 to 2.5:1, (a3) from 0.01 to 10% by weight, based on mixture (a1), of a chain extender from the group consisting of the diisocyanates, divinyl ethers and the 2,2'bisoxazoline of the ##STR8## where R¹ is a single bond, a (CH₂)_(q) alkylene group, where q is 2, 3 or 4, or a phenylene group, or of a mixture of two or more thereof, and (a4) from 0.01 to 20% by weight, based on mixture (a1), of a compound having at least three groups capable of ester formation or of a mixture of two or more thereof, wherein the repeat units derived from (a11) and (a12) form a random distribution, the copolyester has a viscosity number within the range from 5 to 450 ml/g (measured in 50/50 w/w o-dichlorobenzene/phenol at a concentration of 0.5% by weight of copolyester at 25° C.).
 2. A polyester dispersion as claimed in claim 1, wherein the copolyester B comprises as further component(b1) from 0.01 to 100% by weight, based on mixture (a1), of a hydroxycarboxylic acid (b1) defined by the following formula IIa or IIb ##STR9## where p is an integer from I to 1500, r is 1, 2, 3 or 4, and G is phenylene, --(CH₂)_(n) --, where n is 1, 2, 3, 4 or 5, --C(R)H-- or --C(R)HCH₂ --, where R is methyl or ethyl,or of a mixture of two or more thereof.
 3. A polyester dispersion as claimed in claim 1, wherein the proportion of component (a11) is within the range from 40 to 60 mol % and the proportion of component (a12) is within the range from 40 to 60 mol %, in each case based on the total amount of components (a11) to (a13).
 4. A polyester dispersion as claimed in claim 1, wherein (a2) is 1,4-butanediol.
 5. A polyester dispersion as claimed in claim 1, wherein (a3) is hexamethylene diisocyanate.
 6. A process for preparing a polyester dispersion as claimed in claim 1, which comprises(i) preparing a copolyester (B) as defined in claim 1 in a conventional manner by reacting a mixture comprising(a1) a mixture comprising(a11) from 20 to 95 mol % of adipic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof, (a12) from 5 to 80 mol % of terephthalic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof, (a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of two or more thereof, the sum total of the individual mol percentages being 100, (a2) a dihydroxy compound or an aminoalcohol or a mixture of two or more thereof, the molar ratio of (a1) to (a2) being within the range from 0.4:1 to 2.5:1, (a3) from 0.01 to 10% by weight, based on mixture (a1), of a chain extender from the group consisting of the diisocyanates, divinyl ethers and 2,2'bisoxazoline of the ##STR10## where R¹ is a single bond, a (CH₂)_(q) alkylene group, where q is 2, 3 or 4, or a phenylene group, or of a mixture of two or more thereof, and (a4) from 0.01 to 20% by weight, based on mixture (a1), of a compound having at least three groups capable of ester formation or of a mixture of two or more thereof, and performing the reaction in such a way that the repeat units derived from (a11) and (a12) form a random distribution, the copolyester has a viscosity number within the range from 5 to 450 ml/g (measured in 50/50 w/w o-dichlorobenzene/phenol at a concentration of 0.5% by weight of copolyester at 25° C.); (ii) neutralizing and dispersing the resulting copolyester (B) in an aqueous medium using a suitable neutralizer.
 7. A process for preparing a polyester dispersion as claimed in claim 2, which comprises(i) preparing a copolyester (B1) as defined in claim 2 in a conventional manner by reacting a mixture comprising(a1) a mixture comprising(a11) from 20 to 95 mol % of adipic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof, (a12) from 5 to 80 mol % of terephthalic acid or of an ester-forming derivative thereof or of a mixture of two or more thereof, (a13) from 0 to 10 mol % of a sulfonate compound or of a mixture of two or more thereof, the sum total of the individual mol percentages being 100, (a2) a dihydroxy compound or an aminoalcohol or a mixture of two or more thereof, the molar ratio of (a1) to (a2) being within the range from 0.4:1 to 2.5:1, (a3) from 0.01 to 10% by weight, based on mixture (a1), of a chain extender from the group consisting of the diisocyanates, divinyl ethers and the 2,2'bisoxazoline of the ##STR11## where R¹ is a single bond, a (CH₂)_(q) alkylene group, where q is 2, 3 or 4, or a phenylene group, or of a mixture of two or more thereof, and (a4) from 0.01 to 20% by weight, based on mixture (a1), of a compound having at least three groups capable of ester formation or of a mixture of two or more thereof, (b1) from 0.01 to 100% by weight, based on mixture (a1), of a hydroxycarboxylic acid (b1) defined by the following formula IIa or IIb ##STR12## where p is an integer from 1 to 1500, r is 1, 2, 3 or 4, and G is phenylene, --(CH₂)_(n) --, where n is 1, 2, 3, 4 or 5, --C(R)H-- or --C(R)HCH₂ --, where R is methyl or ethyl,or of a mixture of two or more thereof, and performing the reaction in such a way that the repeat units derived from (a11) and (a12) form a random or alternating distribution, the copolyester has a viscosity number within the range from 5 to 450 ml/g (measured in 50/50 w/w o-dichlorobenzene/phenol at a concentration of 0.5% by weight of copolyester at 25° C.); (ii) neutralizing and dispersing the resulting copolyester (B1) in an aqueous medium using a suitable neutralizer.
 8. A process as claimed in claim 6, further comprising dissolving the polyester obtained after step (i) in a suitable organic solvent and removing the same after the neutralizing and dispersing of step (ii).
 9. A nonwoven comprising a binder comprising from 5 to 100% by weight, based on the weight of the fibers used, of a copolyester (B) or of a copolyester (B1) or of a mixture of two or more thereof as defined in claim
 1. 10. A nonwoven as claimed in claim 1, further comprising from 2 to 100% by weight, based on 100 parts by weight of the fibers used, of chitosan.
 11. A process for preparing a nonwoven as claimed in claim 10, which comprises contacting the fibers and a polyester dispersion as defined in claim 1 in a first step in such an amount that the level of copolyester (B) or of copolyester (B1) or of a mixture of two or more thereof in the nonwoven is from 5 to 100% by weight, based on the weight of the fibers used, and, in a further step, preparing an aqueous solution of an acidic salt of chitosan and contacting this solution with the fibers before or after or together with the polyester dispersion in such an amount that the level of chitosan is from 2 to 100% by weight, based on the amount of fibers used.
 12. A process for preparing a nonwoven as claimed in claim 10, which comprises contacting the fibers and the polyester dispersion as defined in claim 12 and, in a further step, preparing an aqueous solution of an acidic salt of chitosan and contacting this solution with the fibers before or after or together with the polyester dispersion in such an amount that the level of chitosan is from 2 to 100% by weight, based on the amount of fibers used.
 13. A process for producing a nonwoven as claimed in claim 10, which comprises contacting the fibers with a polyester dispersion as defined in claim 1 in such an amount that the level of copolyester (B) or of copolyester (B1) or of a mixture of two or more thereof in the nonwoven is from 5 to 100% by weight, based on the weight of the fibers used.
 14. A paper coating comprising as binder a polyester dispersion as defined in claim
 1. 15. A spray mulch obtainable from a polyester dispersion as defined in claim
 1. 16. A polyester dispersion as defined in claim 1, wherein the component (a4) is comprised in an amount of from 1 to 10% by weight, based on mixture (a1).
 17. A process for preparing a polyester dispersion as defined in claim 6, wherein the component (a4) is comprised in an amount of from 1 to 10% by weight, based on mixture (a1).
 18. A process for preparing a polyester dispersion as defined in claim 7, wherein the component (a4) is comprised in an amount of from 1 to 10% by weight, based on mixture (a1). 